Processes for forming aldehydes by the hydroformylation reaction (oxo synthesis) of an olefin with carbon monoxide and hydrogen in the presence of a rhodium complex catalyst and free triarylphosphine are well known in the art.
For instance, U.S. Pat. No. 3,527,809, the entire disclosure of which is incorporated herein, discloses a hydroformylation process where olefins are hydroformylated with carbon monoxide and hydrogen in the presence of a rhodium complex catalyst and free triarylphosphine to produce aldehydes in high yields at low temperatures and pressures, where the normal to iso-(or branch chain) aldehyde isomer ratio of product aldehydes is high.
It is also known that, under hydroformylation conditions, some of the product aldehydes may condense to form by-product, high boiling aldehyde condensation products such as aldehyde dimers or trimers. Commonly-assigned U.S. Pat. No. 4,148,830, the entire disclosure of which is incorporated herein by reference thereto, discloses the use of these high boiling liquid aldehyde condensation products as a reaction solvent for the catalyst. More specifically, as pointed out in said U.S. Pat. No. 4,148,830, some of the aldehyde product is involved in various reactions as depicted below using n-butyraldehyde as an illustration: ##STR1##
In addition, aldol I can undergo the following reaction: ##STR2##
The names in parentheses in the afore-illustrated equations, aldol I, substituted acrolein II, trimer III, trimer IV, dimer V, tetramer VI, and tetramer VII, are for convenience only. Aldol I is formed by an aldol condensation; trimer III and tetramer VII are formed via Tischenko reactions; trimer IV by a transesterification reaction; dimer V and tetramer VI by a disproportionation reaction. Principal condensation products are trimer III, trimer IV, and tetramer VII, with lesser amounts of the other products being present. Such condensation products, therefore, contain substantial quantities of hydroxylic compounds as witnessed, for example, by trimers III and IV and tetramer VII.
Similar condensation products are produced by self-condensation of iso-butyraldehyde and a further range of compounds is formed by condensation of one molecule of normal butyraldehyde with one molecule of iso-butyraldehyde. Since a molecule of normal butyraldehyde can aldolize by reaction with a molecule of iso-butyraldehyde in two different ways to form two different aldols VIII and IX, a total of four possible aldols can be produced by condensation reactions of a normal/iso mixture of butyraldehydes. ##STR3##
Aldol I can undergo further condensation with isobutyraldehyde to form a trimer isomeric with trimer III and aldols VIII and IX and the corresponding aldol X produced by self-condensation of two molecules of isobutyraldehyde can undergo further reactions with either normal or isobutyraldehyde to form corresponding isomeric trimers. These trimers can react further analogously to trimer III so that a complex mixture of condensation products is formed.
In addition commonly-assigned copending U.S. application Ser. No. 776,934, l filed Mar. 11, 1977, now U.S. Pat. No. 4,247,486 (Belgium Patent No. 853,377), the entire disclosure of which is incorporated herein by reference thereto, discloses a liquid phase hydroformylation reaction using a rhodium complex catalyst, wherein the aldehyde reaction products and some of their higher boiling condensation products are removed in vapor form from the catalyst containing liquid body (or solution) at the reaction temperature and pressure. The aldehyde reaction products and the condensation products are condensed out of the off gas from the reaction vessel in a product recovery zone and the unreacted starting materials (e.g., carbon monoxide, hydrogen and/or alpha-olefin) in the vapor phase from the product recovery zone are recycled to the reaction zone. Furthermore, by recycling gas from the product recovery zone coupled with make-up starting materials to the reaction zone in sufficient amounts, it is possible, using a C.sub.2 to C.sub.5 olefin as the alpha-olefin starting material, to achieve a mass balance in the liquid body in the reactor and thereby remove from the reaction zone at a rate at least as great as their rate of formation essentially all the higher boiling condensation products resulting from self-condensation of the aldehyde product.
More specifically, according to said Ser. No. 776,934, a process for the production of an aldehyde containing from 3 to 6 carbon atoms is disclosed which comprises passing an alpha-olefin containing from 2 to 5 carbon atoms together with hydrogen and carbon monoxide at a prescribed temperature and pressure through a reaction zone containing the rhodium complex catalyst dissolved in a liquid body, continuously removing a vapor phase from the reaction zone, passing the vapor phase to a product separation zone, separating a liquid aldehyde containing product in the product separation zone by condensation from the gaseous unreacted starting materials, and recycling the gaseous unreacted starting materials from the product separation zone to the reaction zone.
It is also known in the prior art that even in the absence of intrinsic poisons there may be deactivation of rhodium hydroformylation catalysts under hydroformylation conditions. Copending, commonly-assigned U.S. patent application Ser. No. 762,336 filed Jan. 25, 1977, abandoned in favor of continuation U.S. application No. 151,293 now U.S. Pat. 4,260,828 (Belgium Patent No. 863,268), the entire disclosure of which is incorporated herein by reference thereto, indicates that the deactivation of rhodium hydroformylation catalysts under hydroformylation conditions in the substantial absence of extrinsic poisons is due to the combination of the effects of temperature, phosphine ligand: rhodium mole ratio, and the partial pressures of hydrogen and carbon monoxide and is termed an intrinsic deactivation. It is further disclosed therein that this intrinsic deactivation can be reduced or substantially prevented by establishing and controlling and correlating the hydroformylation reaction conditions to a low temperature, low carbon monoxide partial pressure and high free triarylphosphine ligand:catalytically active rhodium mole ratio.
The manner in which the caron monoxide partial pressure, temperature and free triarylphosphine:catalytically active rhodium mole ratio should be controlled and correlated to thus limit the deactivation of the catalyst is illustrated as follows.
As an example, for the triarylphosphine ligand triphenylphosphine, the specific relationship between these three parameters and catalyst stability is defined by the formula: EQU F=1000/(1+e.sup.y)
where
F=stability factor PA1 e=Naperian log base (i.e., 2.718281828) PA1 y=K.sub.1 +K.sub.2 T+K.sub.3 P+K.sub.4 (L/Rh) PA1 T=reaction temperature (.degree.C.) PA1 P=partial pressure of CO (psia) PA1 L/Rh=free triarylphosphine:catalytically active rhodium mole ratio PA1 K.sub.1 =-8.1126 PA1 K.sub.2 =0.07919 PA1 K.sub.3 =0.0278 PA1 K.sub.4 =-0.01155
As pointed out in said Ser. No. 762,336, an olefin response factor must be employed to obtain the stability factor under actual hydroformylation conditions. Olefins generally enhance the stability of the catalyst and their effect on catalyst stability is more fully explained in said application. The above relationship is substantially the same for other triarylphosphines, except that the constants K.sub.1, K.sub.2, K.sub.3 and K.sub.4 may be different. Those skilled in the art can determine the specific constants for other triarylphosphines with a minimum amount of experimentation as explained more fully in said application.
It has also been observed that the presence of an alkyldiarylphosphine (for example, propyldiphenylphosphine or ethyldiphenylphosphine) in the rhodium-catalyzed hydroformylation of the alpha-olefin propylene inhibits catalyst productivity; i.e., the rate at which the desired product aldehydes are formed. Specifically, the addition of small amounts of propyldiphenylphosphine or ethyldiphenylphosphine to rhodium hydroformylation solutions markedly reduced the rate of production of butyraldehydes from propylene, compared to the rate obtained in the absence of the alkyldiarylphosphines.
Although the presence of alkyldiarylphosphines in rhodium-catalyzed hydroformylation processes reduces the catalyst productivity, the stability of such rhodium complex catalysts can be enhanced by providing an alkyldiarylphosphine in the reaction medium and copending, commonly assigned U.S. application Ser. No. 762,335 filed Jan. 25, 1977, abandoned in favor of continuation U.S. application 140,380 filed Apr. 16, 1980 (Belgium Patent 863,267), the entire disclosure of which is incorporated herein by reference thereto, teaches that the reaction conditions can be adjusted to be more severe in order to regain this apparent loss of catalyst productivity while retaining the enhanced catalyst stability.
Said Ser. No. 762,335 further teaches that when a triarylphosphine ligand is employed in the hydroformylation of an alpha-olefin, some alkyldiarylphosphine is produced in situ, the "alkyl" group thereof being derived from the alpha-olefin undergoing hydroformylation and the "aryl" groups thereof being the same as the aryl of the triarylphosphine.
Said Ser. No. 762,335 further discloses that when an alkyldiarylphosphine ligand is present in a liquid reaction medium containing a rhodium complex catalyst consisting essentially of rhodium complexed with carbon monoxide and a triarylphosphine ligand, the resulting rhodium complex catalyst consists essentially of rhodium complexed with carbon monoxide and either one or both of the triarylphosphine ligand and the alkyldiarylphosphine ligand and that the terminology "consists essentially of" is not meant to exclude, but rather to include, hydrogen complexed with the rhodium, in addition to carbon monoxide and triarylphosphine and/or alkyldiarylphosphine. However, this language is meant to exclude other materials in amounts which poison or deactivate the catalyst. Said Ser. No. 762,335 goes on to disclose that particularly advantageous results are achieved when the amount of total free phosphine ligand in the liquid reaction medium is at least about 100 moles per mole of catalytically-active rhodium metal present in the rhodium complex catalyst.
Thus it is known that, despite the obvious advantages of the above inventions, during use the rhodium complex catalyst loses activity (i.e. becomes partially deactivated) and eventually, after prolonged use, the activity of the catalyst will have decreased to such a point that it is no longer economically desirable to operate the hydroformylation process and the catalyst will have to be discharged and replaced with fresh catalyst. Accordingly, due to the high cost of rhodium values the reactivation of such partially deactivated catalysts and/or recovery of the rhodium values of such catalysts is of extreme importance to the state of the art.